1. Field of the Invention
The present invention relates to a thrust reverser for a turbofan-type engine in which a pivotable flap redirects the direction of the flow of gases passing through an annular duct to provide thrust reversing forces. More particularly, the present invention relates to a thrust reverser having a displaceable assembly including a displaceable cowling portion that forms a portion of an external fan cowling in a forward thrust position and extends downstream, parallel to the engine axis so as to form an opening in the external fan cowling in a reverse thrust position, and a pivotable flap that forms a portion of the outer boundary of the gas flow duct in a forward thrust position, and cooperates with the displaceable cowling portion and pivots so as to deflect the gas flow through the external cowling opening in a reverse thrust position.
2. Related Art
Turbofan-type turbojet engines are well-known in the art and comprise an annular duct to the rear of the fan for the purpose of channeling the so-called cold, bypass flow. This annular duct is bounded on the inside by the engine cowling and on the outside by a fan cowling. The annular duct may channel both the bypass flow and the primary exhaust gas flow at a downstream portion, or may channel only the bypass flow. It is known to provide one or more pivotable flaps in the annular duct to redirect the cold flow gas laterally outwardly through a lateral opening in the cowling.
FIGS. 1 through 10 show a known pivoting door-type thrust reverser associated with the fan cowling of a turbofan-type engine.
As illustrated in FIGS. 3 and 4, the thrust reverser is a so-called vane-cascade reverser wherein a displaceable assembly 1 in a forward-thrust position comprises a portion of the outer boundary of the annular duct 2 that channels the bypass flow. In a reverse thrust position, the thrust reverser door is axially displaceable in the downstream direction by a control system comprising a set of linear actuators 3 which are affixed on the upstream portion 4 of the thrust reverser. As shown in FIGS. 2 and 4, the downstream displacement of the displaceable assembly 1 entails pivoting a plurality of flaps 5 which are arranged to seal the duct and deflect the gas flow, thus providing a reverse flow which is guided by a cascade of vanes 23 configured on the external periphery of the duct and exposed to the deflected gas flow in a reverse thrust position.
The known designs of such a turbojet-engine thrust reverser comprise two parts, each part comprising a semi-cylindrical segment of the displaceable assembly 1 and driven, by linear actuators 3. The pivoting motion of flaps 5 are guided by linkrods 6 about a fixed linkrod hinge point 7 which is arranged on the inside wall 8 of the bypass duct.
European patent document 0 109 219 A and U.S. Pat. No. 3,500,645 illustrate typical known thrust reversers. Such known designs of thrust reversers have led to a number of inadequately resolved problems. For example, the attempts to reduce weight affect the rigidity of the displaceable assembly 1. As a result, the exhaust cross-section may become aerodynamically unstable.
As illustrated in FIGS. 6-10, displacement of the displaceable assembly 1 requires that the primary rails 9, of which the lengths protrude beyond the pod lines in the external and internal zones 11 and 12 respectively shown in FIG. 10 be smoothed by either external fairings 13 or by internal fairings 14. Moreover, secondary rails 16 are required for guidance and structural reinforcement of the external flap 15 of the displaceable assembly 1. The displaceable assembly 1 is arranged with bays 17 to access the linear actuators 3. The force exerted by the linear actuators 3 is applied to fittings 19 situated at the rear portion of the displaceable assembly 1.
As shown in FIGS. 6-8, the flaps 5 hinge on fittings 19 resting on the internal panel 20 of the displaceable assembly 1. The flaps 5 exhibit a contour that follows the routings 21 so they will not interfere in the thrust-reversal mode. However, flap corners 22 are required to fill the gaps that arise in the forward-thrust position.
The object of this invention are to eliminate the drawbacks of the known prior solutions of thrust reversers provided with the conventional above cited vane cascades while providing simplified manufacture, weight reduction and improvement of aerodynamic performance.
The present invention realizes the objective by providing a thrust reverser of the type cited above wherein in a forward thrust position, a displaceable cowling portion and a flap, belonging to at least one displaceable assembly, each subtend the upstream and downstream cowling portions such that the displaceable cowling portion forms a portion of the external fan cowling covering a reverse thrust opening and the flap forms a portion of the outer boundary of the gas flow. In a reverse thrust position, the reverse thrust opening is uncovered, and the displaceable cowling portion and the flap are displaced downstream such that the displaceable cowling portion extends downstream, parallel to the longitudinal engine axis and above, without interference, the downstream cowling portion. The flap engages in rolling contact with a plurality of rolling elements supported by an upstream end of the stationary downstream cowling portion and pivots and so as to block the gas flow duct and redirect the gas flow outward through the vane-cascades.
Several supplementary design configurations relate to driving the flaps.